Heterogeneity in transmissibility and shedding SARS-CoV-2 via droplets and aerosols

Chen, P. Z.; Bobrovitz, N.; Premji, Z.; Koopmans, M.; Fisman, D. N.; Gu, F. X.

A growing number of studies provide insight into how SARS-CoV-2 spreads1-7. Yet, many factors that characterize its transmissibility remain unclear, including mechanistic correlates of overdispersion, viral kinetics, the extent to which respiratory droplets and aerosols carry viable virus and the infectiousness of asymptomatic, presymptomatic and pediatric cases7. Here, we developed a comprehensive dataset of respiratory viral loads (rVLs) via systematic review and investigated these factors using meta-analyses and modeling. By comparing cases of COVID-19, SARS and influenza A(H1N1)pdm09, we found that heterogeneity in rVL was associated with overdispersion and facilitated the distinctions in individual variation in infectiousness among these emergent diseases. For COVID-19, case heterogeneity was broad throughout the infectious period, although rVL tended to peak at 1 day from symptom onset (DFSO) and be elevated for 1-5 DFSO. While most cases presented minimal risk, highly infectious ones could spread SARS-CoV-2 by talking, singing or breathing, which shed virions at comparable rates via droplets and aerosols. Coughing shed considerable quantities of virions, predominantly via droplets, and greatly increased the contagiousness of many symptomatic cases relative to asymptomatic ones. Asymptomatic and symptomatic infections showed similar likelihoods of expelling aerosols with SARS-CoV-2, as did adult and pediatric cases. Children tended to be less contagious by droplet spread than adults based on tendencies of symptomatology rather than rVL. Our findings address longstanding questions on SARS-CoV-2 transmissibility and present pertinent considerations for disease control.